Impaired serotonin (5-HT) function has been implicated as a possible factor in the biological vulnerability for alcoholism, but most studies of the 5-HT system have been performed in animals or, if performed in humans, they involved only indirect measurements to assess the 5-HT system in the brain. The status of the 5-HT neurons in the brain of living alcohol dependent individuals remains unknown. To investigate the 5-HT system of the brain, quantitative PET studies of the brain 5-HT transporter (5-HTT; an established marker of serotonin neuron integrity) are proposed using [11C]McN5652 as radioligand for four groups of human subjects: family negative (FHN) controls, family history positive (FHP) controls, FHN recovering alcoholics, and FHP recovering alcoholics. The hypothesis to be tested is that radioligand binding to the 5-HT transporter is significantly reduced as a function of both alcoholism and family history of alcoholism. Serotonin function will also be measured by quantification of plasma prolactin and cortisol increase in response to fluoxetine. The genetic aspect of 5-HT impairment will be investigated by measuring the frequency of specific polymorphisms of the 5-HTT gene. The hypothesis is that FHP alcoholics and FHP controls will have a higher frequency of the s-variant allele, the allele, which has been associated with reduced 5-HTT expression/function in in vitro studies. The frequency of the s-variant allele is predicted to be higher in subjects with reduced 5-HTT densities (as determined by PET) and with reduced hormonal responses to fluoxetine. The results of this project will lead to better understanding of the role of serotonin in the biological vulnerability for alcoholism and may lead to improved approaches to prevent and treat alcoholism.